Implantable medical device having flat electrolytic capacitor fabricated with laser welded anode sheets

ABSTRACT

Implantable medical devices (IMDs) and components, including flat electrolytic capacitors and methods of making and using same, particularly an improved electrolytic capacitor fabricated of an electrode stack assembly comprising a plurality of capacitor layers stacked in registration upon one another. Each capacitor layer comprises a valve metal cathode layer having a cathode tab, a valve metal anode layer having an anode tab, and a separator layer located between the cathode layers. The anode layer is assembled from a plurality of valve metal anode sheets that are etched and anodized, stacked side-by-side, and electrically and mechanically joined together by laser weld beads. A valve metal anode tab having a thickness equal to one or more anode sheet is inserted into a tab notch in one or more stacked anode sheet and joined to the anode sheet stack by laser welding the tab and sheet edges together.

FIELD OF THE INVENTION

This invention relates to implantable medical devices (IMDs) and theirvarious components, including flat electrolytic capacitors for same, andmethods of making same, particularly such capacitors assembled from aplurality of stacked capacitor layers each having anode layers assembledfrom a plurality of formed valve metal anode sheets.

BACKGROUND OF THE INVENTION

A wide variety of IMDs are known in the art. Of particular interest areimplantable cardioverter-defibrillators (ICDs) that deliver relativelyhigh-energy cardioversion and/or defibrillation shocks to a patient'sheart when a malignant tachyarrhythmia, e.g., atrial or ventricularfibrillation, is detected. The shocks are developed by discharge of oneor more high voltage electrolytic capacitor that is charged up from anICD battery. Current ICDs typically possess single or dual chamberpacing capabilities for treating specified chronic or episodic atrialand/or ventricular bradycardia and tachycardia and were referred topreviously as pacemaker/cardioverter/defibrillators (PCDs). Earlierdeveloped automatic implantable defibrillators (AIDs) did not havecardioversion or pacing capabilities. For purposes of the presentinvention ICDs are understood to encompass all such IMDs having at leasthigh voltage cardioversion and/or defibrillation capabilities.

Energy, volume, thickness and mass are critical features in the designof ICD implantable pulse generators (IPGs) that are coupled to the ICDleads. The battery(s) and high voltage capacitor(s) used to provide andaccumulate the energy required for the cardioversion/defibrillationshocks have historically been relatively bulky and expensive. Presently,ICD IPGs typically have a volume of about 40 to about 60 cc, a thicknessof about 13 mm to about 16 mm and a mass of approximately 100 grams.

It is desirable to reduce the volume, thickness and mass of suchcapacitors and ICD IPGs without reducing deliverable energy. Doing so isbeneficial to patient comfort and minimizes complications due to erosionof tissue around the ICD IPG. The high voltage capacitor(s) are amongthe largest components that must be enclosed within the ICD IPG housing.Reductions in size of the capacitors may also allow for the balancedaddition of volume to the battery, thereby increasing longevity of theICD IPG, or balanced addition of new components, thereby addingfunctionality to the ICD IPG. It is also desirable to provide such ICDIPGs at low cost while retaining the highest level of performance. Atthe same time, reliability of the capacitors cannot be compromised.

Various types of flat and spiral-wound capacitors are known in the art,some examples of which are described as follows and/or may be found inthe patents listed in Table 1 of commonly assigned U.S. Pat. No.6,006,133. Typically, an electrolytic capacitor is fabricated with acapacitor case enclosing a “valve metal” (e.g., aluminum) anode layer(or “electrode”), a valve metal (e.g. aluminum) cathode layer (or“electrode”), and a Kraft paper or fabric gauze spacer or separatorimpregnated with a solvent based liquid electrolyte interposedtherebetween. The aluminum anode layer is typically fabricated fromaluminium foil that is first etched and then “formed” by passage ofelectrical current through the anode layer to oxidize the etchedsurfaces so that the aluminium oxide functions as a dielectric layer.The electrolyte comprises an ion producing salt that is dissolved in asolvent and provides ionic electrical conductivity between the cathodelayer and the aluminum oxide dielectric layer. The energy of thecapacitor is stored in the electromagnetic field generated by opposingelectrical charges separated by the aluminum oxide layer disposed on thesurface of the anode layer and is proportional to the surface area ofthe etched aluminum anode layer. Thus, to minimize the overall volume ofthe capacitor one must maximize anode surface area per unit volumewithout increasing the capacitor's overall (i.e., external) dimensions.The separator material, anode and cathode layer terminals, internalpackaging, electrical interconnections, and alignment features andcathode material further increase the thickness and volume of acapacitor. Consequently, these and other components in a capacitor andthe desired capacitance limit the extent to which its physicaldimensions may be reduced.

Some ICD IPGs employ commercial photoflash capacitors similar to thosedescribed by Troup in “Implantable Cardioverters and Defibrillators,”Current Problems in Cardiology, Volume XIV, Number 12, December 1989,Year Book Medical Publishers, Chicago, and as described in U.S. Pat. No.4,254,775. The electrodes or anode and cathodes are wound into anode andcathode layers separated by separator layers of the spiral. Mostcommercial photoflash capacitors contain a core of separator paperintended to prevent brittle, highly etched aluminum anode foils fromfracturing during winding of the anode, cathode, and separator layersinto a coiled configuration. The cylindrical shape and paper core ofcommercial photoflash capacitors limits the volumetric packagingefficiency and thickness of an ICD IPG housing made using same.

More recently developed ICD IPGs employ one or more flat or “prismatic”,high voltage, electrolytic capacitor to overcome some of the packagingand volume disadvantages associated with cylindrical photoflashcapacitors. Flat aluminum electrolytic capacitors for use in ICD IPGshave been disclosed, e.g., those improvements described in “High EnergyDensity Capacitors for Implantable Defibrillators” presented by P.Lunsmann and D. MacFarlane at CARTS 96: 16th Capacitor and ResistorTechnology Symposium, 11-15 Mar. 1996, and at CARTS-EUROPE 96: 10thEuropean Passive Components Symposium., 7-11 Oct. 1996, pp. 35-39.Further features of flat electrolytic capacitors for use in ICD IPGs aredisclosed in U.S. Pat. Nos. 4,942,501; 5,086,374; 5,131,388; 5,146,391;5,153,820; 5,522,851, 5,562,801; 5,628,801; and 5,748,439, all issued toMacFarlane et al.

For example, U.S. Pat. Nos. 5,131,388 and 5,522,851 disclose a flatcapacitor having a plurality of stacked capacitor layers each comprisingan “electrode stack sub-assembly”. Each capacitor layer contains one ormore anode sheet forming an anode layer having an anode tab, a cathodesheet or layer having a cathode tab and a separator for separating theanode layer from the cathode layer.

Electrical performance of such electrolytic capacitors is affected bythe surface area of the anode and cathode layers and also by theresistance associated with the electrolytic capacitor itself, called theequivalent series resistance (ESR). The ESR is a “hypothetical” seriesresistance that represents all energy losses of an electrolyticcapacitor regardless of source. The ESR results in a longer charge time(or larger build factor) and lower discharge efficiency. Therefore, itis desirable to reduce the ESR to a minimum.

Typically, ESR is minimized by fabricating the anode layer of eachcapacitor layer from highly etched valve metal foil, e.g., aluminumfoil, that has a microscopically contoured, etched surface with a highconcentration of pores extending part way through the anode foil alongwith tunnels extending all the way through the anode foil(through-etched or tunnel-etched) or only with a high concentration ofpores extending part way through the anode foil (nonthrough-etched. Ineither case, such a through-etched or nonthrough-etched anode sheet cutfrom such highly etched foil exhibit a total surface area much greaterthan its nominal (length times width) surface area. A surface areacoefficient, the ratio of the microscopic true surface area to themacroscopic nominal area, may be as high as 100:1, which advantageouslyincreases capacitance. Through-etched or tunnel-etched anode sheetsexhibit a somewhat lower ratio due to the absence of a web or barriersurface closing the tunnel as in nonthrough-etched anode sheets.

After the aluminum foil is etched, the aluminum oxide layer on theetched surface is “formed” by applying voltage to the foil through anelectrolyte such as boric acid or citric acid and water or othersolutions familiar to those skilled in the state of the art. Typically,individual anode sheets are punched, stamped or otherwise cut out of thefoil in a shape to conform to the capacitor package following formationof the aluminum oxide on the foil. The cut edges around the periphery ofthe anode sheets are carefully cleaned to remove particulates of anodematerial that can get caught between the capacitor layers in theelectrode stack assembly resulting in a high leakage current orcapacitor failure. Anode layers comprise either a single anode sheet ormultiple anode sheets. Stacking the anode layer, separator layers, andcathode layer together assembles capacitor layers, and electrode stackassemblies are assembled by stacking a plurality of capacitor layerstogether, separated by separator layers. The cut edges of the anode andcathode layers and any other exposed aluminum are then reformed in thecapacitor during the aging process to reduce leakage current. In orderto increase capacitance (and energy density), multiple anode sheets arestacked together to form the multiple sheet anode layer as describedabove. Through-etched or tunnel-etched anode sheets need to be used insuch multiple sheet anode layers to ensure that electrolyte isdistributed over all of the aluminum oxide layers of the sandwichedinner anode sheets and to provide a path for ionic communication. But,then the gain in surface area is not as high as that which can beachieved with a like number of stacked nonthrough-etched anode sheetsthat have a remaining solid section in their center.

For example, the '890 patent discloses the use of an anode layerfabricated from a highly etched center sheet with a solid core and twotunnel-etched anode sheets sandwiching the center sheet. Thisarrangement is intended to allow the electrolyte, and thus theconducting ions, to reach all surface areas of the three-sheet anodelayer while preventing the ions from passing all the way through theanode layer. More than three tunnel etched anode sheets can be used inthe anode layer depending on the desired electrical performance.

The aluminum oxide layers electrically isolate the aluminum sheets ofthe aluminum layer from each other, and an electrical connection must bemade between the underlying aluminum valve metal of each anode sheet ofthe anode layer. In one approach, each anode sheet of each anode layeris fabricated with an outwardly projecting anode tab. The tabs of theanode layers and the cathode layers of all of the capacitor layers ofthe stack are electrically connected in parallel to form a singlecapacitor or grouped to form a plurality of capacitors. The attachedaluminum anode sheet tabs are electrically connected to a feedthroughpin of an anode feedthrough extending through the case or compartmentwall. The anode tabs that are fabricated integrally with the anodesheets are also etched and anodized with the anode sheets and renderedbrittle making it difficult to bend the anode tabs together or towardone unless the tab areas are masked during etching. In theabove-referenced '851 patent, each of the anode sheet tabs are weldedtogether and then welded to a post of a feedthrough pin. The singlesheet cathode layers are also fabricated with cathode tabs that are alsogathered together and electrically connected to a feedthrough pin of acathode feedthrough extending through the case or compartment wall orconnected to the electrically conductive capacitor case wall. Thebending of the tabs is minimized but they take up space.

In a further approach disclosed in U.S. Pat. No. 6,191,931, a flatcapacitor is assembled from a stack of anode layers and cathode sheetsseparated from one another by a separator. Each of the anode layers is asingle anode sheet, and anode tabs and cathode tabs are integrally partof the respective anode and cathode sheets. Separators are insertedbetween each of the anode layers and cathode layers. The edges of theanode and cathode layers and separators are taped together to hold themin alignment. Then, at least the anode tabs are brought together andlaser welded to one another and to a feedthrough wire. The anode tabsare fabricated with wire receiving weld notches in the tab ends so thatthe wire can be fitted into the weld notches to extend normally to thebrought together stack of anode tabs. The wire is then laser welded inthat position. An electrical connection of the stacked anode layers ismade in this way through the welded wire and tab of each single sheet,anode layer. The laser weld does not hold the stacked assembly togetheror couple anode sheets together into an anode layer.

In further U.S. Pat. No. 6,319,292, a porous pellet capacitor anode isprepared for welding of an anode tab by laser welding a surface area tofuse that area. The anode tab is then welded to the prepared area.

Capacitor volume can be reduced slightly by interposing and welding ashared anode tab in between two adjacent anode sheets in the anodestack, as described, for example, in the above-referenced '388 patent.No particular method of welding is disclosed, and the interposed stackof anode tabs would thicken and distort the anode sheet stack making itdifficult to fit into a flat-sided capacitor housing.

In another approach described in U.S. Pat. No. 5,584,890, the centeranode sheet of a three-sheet anode layer is fabricated with an inwardrecess into which an anode tab is inserted. The three anode sheets arejoined together at a distance from the anode tab by using cold welding,although laser welding and arc welding are mentioned as alternativeswithout detail.

In the above-referenced '133 patent, a single anode tab is fitted into aslot of one of the stacked anode sheets and attached to one or more ofthe adjoining anode sheets by cold welding. The anode sheets are coldwelded together at more than one location by use of a press and pressfixture having spring-loaded or pneumatically driven cold weld pins thatextend through pin bores of a top plate and a base plate bearing againstthe uppermost and lowermost exposed surfaces of the stack of anodesheets to be cold welded together.

By necessity, the joinder of anode sheets together to form multi-sheetanode layers and to separate anode tabs by such techniques must breakthrough the oxide layer over the exposed etched surfaces of the anodesheets and fill or compress the underlying etched surface until thevalve metals of the sheet cores are in intimate contact such that a lowresistance electrical connection is achieved. Typically, it is necessaryto provide multiple attachment sites to provide redundancy, whichincreases reliability. But breaking through the etched oxide layers ofthe multiple sheets in multiple places reduces the overall capacitance.Moreover, the attachment techniques can damage the etched oxide layersadjacent to the points of attachment or across the exposed outermostsurfaces of the outermost sheets of the anode layer.

Thus, there is a need for further reducing capacitor volume, increasingcapacitor reliability, and reducing cost and complexity of the capacitormanufacturing process, for multi-sheet anode layer capacitors used inICDs and other IMDs and other electric circuit applications.

SUMMARY OF THE INVENTION

The present invention provides for methods and apparatus for securelymechanically and electrically attaching anode sheets of multi-sheetanode layers of electrolytic capacitors together in a simple manner thatdoes not without unduly damage adjacent or exposed oxide layers.

In accordance with the present invention, the anode layer is assembledfrom a plurality of valve metal anode sheets that are etched and“formed”, stacked side-by-side, and then electrically and mechanicallyjoined together by at least one and preferably a plurality of laser weldbeads extending across the edges of the stacked anode sheets.

In one embodiment, the edges of the anode sheets are notched with weldnotches to receive reinforcing weld wires or strips that are laserwelded to the core layers of the notched anode sheets.

In another embodiment, a valve metal anode tab having a thickness equalto one or more anode sheet is inserted into a tab notch in one or morestacked anode sheet and joined to the anode sheet stack by laser weldingthe anode tab edge and the sheet edges together.

Advantageously, a robust electrical and mechanical connection of theanode sheets of the anode layer is achieved through the presentinvention. Compression and damage of the etched and anodized layers ofthe anode sheets is minimized, and a high capacitance per unit area isachieved.

A capacitor is assembled from an electrode stack assembly comprising atleast one anode layer, cathode layer, and separator between the anodelayer and the cathode layer and fitted into a capacitor case withappropriate electrical connectors to the anode and cathode layers. Or, acapacitor layer is assembled from the anode layer, a cathode layer, anda separator between the anode layer and the cathode layer, and aplurality of the cathode layers are stacked into a capacitorsub-assembly, electrically interconnected and fitted into a capacitorcase with appropriate electrical connectors to the anode and cathodelayers.

In one embodiment, an exemplary electrolytic capacitor fabricated inaccordance with the present invention comprises an electrode stackassembly and electrolyte located within the interior case chamber of ahermetically sealed capacitor case. The electrode stack assemblycomprises a plurality of capacitor layers stacked in registration uponone another, each capacitor layer comprising a cathode layer having acathode tab, an anode layer comprising at least one anode sheet havingan anode tab, and a separator layer located between adjacent anode andcathode layers, whereby all adjacent cathode layers and anode layers ofthe stack are electrically insulated from one another by a separatorlayer. Anode terminal means extend through the capacitor case sidewallfor electrically connecting a plurality of the anode tabs to one anotherand providing an anode connection terminal at the exterior of the case.Cathode terminal means extend through or to an encapsulation area of thecapacitor case side wall for electrically connecting a plurality of thecathode tabs to one another and providing a cathode connection terminalat the exterior of the case. A connector assembly is electricallyattached to the anode connection terminal for making electricalconnection with the anode tabs and to the cathode connection terminalfor making electrical connection with the cathode tabs.

In another embodiment, the electrode stack assembly is formed of ananode layer formed of many stacked and laser welded anode sheets with acathode layer wrapped substantially around the anode layer and aseparator between the anode and cathode layer.

This summary of the invention and the advantages and features thereofhave been presented here simply to point out some of the ways that theinvention overcomes difficulties presented in the prior art and todistinguish the invention from the prior art and is not intended tooperate in any manner as a limitation on the interpretation of claimsthat are presented initially in the patent application and that areultimately granted.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and features of the present invention will beappreciated as the same becomes better understood by reference to thefollowing detailed description of the preferred embodiment of theinvention when considered in connection with the accompanying drawings,in which like numbered reference numbers designate like parts throughoutthe figures thereof, and wherein:

FIG. 1 illustrates the physical components of one exemplary embodimentof an ICD IPG and lead system in which the present invention may beadvantageously incorporated;

FIG. 2 is a simplified functional block diagram illustrating theinterconnection of voltage conversion circuitry with the high voltagecapacitors of the present invention with the primary functionalcomponents of one type of an ICD;

FIGS. 3(a)-3(g) are exploded perspective views of the manner in whichthe various components of the exemplary ICD IPG of FIGS. 1 and 2,including the electrolytic capacitors of the present invention, aredisposed within the housing of the ICD IPG;

FIG. 4 is an exploded view of one embodiment of a single capacitor layerof an electrolytic capacitor incorporating the present invention;

FIG. 5 is a flow chart illustrating the steps of forming an electrolyticcapacitor in accordance with the invention;

FIG. 6 is a perspective view of the anode layer assembled from anodesheets employing laser weld beads in a plurality of spaced apart narrowbands across the aligned edges of the anode sheet stack to weld theanode sheets together in accordance with the preferred embodiments ofthe invention;

FIG. 7 is a partial perspective schematic illustration of firstplurality of bands of laser weld beads extending across the alignededges of the anode sheet stack to weld the anode sheets together and asecond plurality of bands of laser weld beads extending across thealigned edges of the anode sheet stack and an anode tab inserted intoone or more aligned tab notch in one or more of the anode sheets to weldthe anode tab to the anode sheets;

FIG. 8(a) is a partial perspective schematic illustration of amodification of the embodiment of FIG. 7 wherein the first plurality ofbands of laser weld beads extending across the aligned edges of theanode sheet stack and over weld strips or wires interposed in alignedweld notches of the edges of the anode sheets to weld the anode sheetstogether;

FIG. 8(b) is a partial end schematic illustration of a variation of FIG.8(a) wherein the weld beads each can comprise a pair of weld beadsformed of melt portions of the wire in the aligned weld notches and theadjoining anode sheet edges;

FIG. 9 is an exploded top perspective view of one embodiment of a seriesof capacitor layers each incorporating the anode layers of the presentinvention ready to be assembled into a electrode stack assembly andfitted together with the remaining components of one embodiment of anelectrolytic capacitor;

FIG. 10 is an exploded top perspective view of the electrode stackassembly ready to be fitted together with the remaining components ofthe embodiment of an electrolytic capacitor;

FIG. 11 is a plan view of the electrode stack assembly fitted into thecapacitor housing together and attached to the remaining components ofthe embodiment of an electrolytic capacitor prior to attaching the coverto the housing and filling the capacitor with electrolyte;

FIG. 12 is a plan view of the completed embodiment of an electrolyticcapacitor in accordance with the invention; and/

FIG. 13 is a perspective view in partial section of a further electrodestack assembly formed in accordance with the teachings of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention is described herein inrelation to an ICD IPG without limitation as to other uses ofelectrolytic capacitors fabricated in accordance with the generalprinciples of the invention. The following described capacitor and ICDtakes the overall form of those disclosed in the above-referenced,commonly assigned '133 and related patents, but the present inventioncan be employed in the fabrication of electrolytic capacitors of anyconfiguration used in ICDs, other IMDs and in other applications. Whilethe present invention can be practiced using valve metals of any type,aluminum is employed in the preferred embodiments described herein.

FIG. 1 illustrates one embodiment of ICD IPG 10 in which the capacitorof the present invention is advantageously incorporated, the associatedICD electrical leads 14, 16 and 18, and their relationship to a humanheart 12. The leads are coupled to ICD IPG 10 by means of multi-portconnector block 20, which contains separate connector ports for each ofthe three leads illustrated. Lead 14 is coupled to subcutaneouselectrode 30, which is intended to be mounted subcutaneously in theregion of the left chest. Lead 16 is a coronary sinus lead employing anelongated coil electrode, which is located in the coronary sinus andgreat vein region of the heart. The location of the electrode isillustrated in broken line format at 32, and extends around the heartfrom a point within the opening of the coronary sinus to a point in thevicinity of the left atrial appendage.

Lead 18 is provided with elongated electrode coil 28, which is locatedin the right ventricle of the heart. Lead 18 also includes stimulationelectrode 34 that takes the form of a helical coil that is screwed intothe myocardial tissue of the right ventricle. Lead 18 may also includeone or more additional electrodes for near and far field electrogramsensing.

In the system illustrated, cardiac pacing pulses are delivered betweenhelical electrode 34 and elongated electrode 28. Electrodes 28 and 34are also employed to sense electrical signals indicative of ventricularcontractions. As illustrated, it is anticipated that the rightventricular electrode 28 will serve as the common electrode duringsequential and simultaneous pulse multiple electrode defibrillationregimens. For example, during a simultaneous pulse defibrillationregimen, pulses would simultaneously be delivered between electrode 28and electrode 30 and between electrode 28 and electrode 32. Duringsequential pulse defibrillation, it is envisioned that pulses would bedelivered sequentially between subcutaneous electrode 30 and electrode28 and between coronary sinus electrode 32 and right ventricularelectrode 28. Single pulse, two electrode defibrillation shock regimensmay be also provided, typically between electrode 28 and coronary sinuselectrode 32. Alternatively, single pulses may be delivered betweenelectrodes 28 and 30. The particular interconnection of the electrodesto an ICD will depend somewhat on which specific single electrode pairdefibrillation shock regimen is believed more likely to be employed.

FIG. 2 is a block diagram illustrating the interconnection of highvoltage output circuit 40, high voltage charging circuit 64 andcapacitors 265 according to one example of the microcomputer basedoperating system of the ICD IPG of FIG. 1. As illustrated, the ICDoperations are controlled by means of a stored program in microprocessor42, which performs all necessary computational functions within the ICD.Microprocessor 42 is linked to control circuitry 44 by means ofbi-directional data/control bus 46, and thereby controls operation ofthe output circuitry 40 and the high voltage charging circuitry 64.Pace/sense circuitry 78 awakens microprocessor 42 to perform anynecessary mathematical calculations, to perform tachycardia andfibrillation detection procedures and to update the time intervalscontrolled by the timers in pace/sense circuitry 78 on reprogramming ofthe ICD operating modes or parameter values or on the occurrence ofsignals indicative of delivery of cardiac pacing pulses or of theoccurrence of cardiac contractions.

The basic operation and particular structure or components of theexemplary ICD of FIGS. 1 and 2 may correspond to any of the systemsknown in the art, and the present invention is not dependent upon anyparticular configuration thereof. The flat aluminum electrolyticcapacitor of the present invention may be employed generally inconjunction with the various systems illustrated in the aforementioned'209 patent, or in conjunction with the various systems or componentsdisclosed in the various patents listed in the above-referenced '133patent.

Control circuitry 44 provides three signals of primary importance tooutput circuitry 40. Those signals include the first and second controlsignals discussed above, labelled here as ENAB, line 48, and ENBA, line50. Also of importance is DUMP line 52, which initiates discharge of theoutput capacitors, and VCAP line 54 that provides a signal indicative ofthe voltage stored on the output capacitors C1, C2, to control circuitry44. Defibrillation electrodes 28, 30 and 32 illustrated in FIG. 1,above, are shown coupled to output circuitry 40 by means of conductors22, 24 and 26. For ease of understanding, those conductors are alsolabelled as “COMMON”, “HVA” and “HVB”. However, other configurations arealso possible. For example, subcutaneous electrode 30 may be coupled toHVB conductor 26, to allow for a single pulse regimen to be deliveredbetween electrodes 28 and 30. During a logic signal on ENAB, line 48, acardioversion/defibrillation shock is delivered between electrode 30 andelectrode 28. During a logic signal on ENBA, line 50, acardioversion/defibrillation shock is delivered between electrode 32 andelectrode 28.

The output circuitry includes a capacitor bank, including capacitors C1and C2 and diodes 121 and 123, used for delivering defibrillation shocksto the electrodes. Alternatively, the capacitor bank may include afurther set of capacitors as depicted in the above referenced '758application. In FIG. 2, capacitors 265 are illustrated in conjunctionwith high voltage charging circuitry 64, controlled by thecontrol/timing circuitry 44 by means of CHDR line 66. As illustrated,capacitors 265 are charged by means of a high frequency, high voltagetransformer 65. Proper charging polarities are maintained by means ofthe diodes 121 and 123. VCAP line 54 provides a signal indicative of thevoltage on the capacitor bank, and allows for control of the highvoltage charging circuitry and for termination of the charging functionwhen the measured voltage equals the programmed charging level.

Pace/sense circuitry 78 includes an R-wave sense amplifier and a pulsegenerator for generating cardiac pacing pulses, which may alsocorrespond to any known cardiac pacemaker output circuitry and includestiming circuitry for defining ventricular pacing intervals, refractoryintervals and blanking intervals, under control of microprocessor 42 viacontrol/data bus 80.

Control signals triggering generation of cardiac pacing pulses bypace/sense circuitry 78 and signals indicative of the occurrence ofR-waves, from pace/sense circuitry 78 are communicated to controlcircuitry 44 by means of a bi-directional data bus 81. Pace/sensecircuitry 78 is coupled to helical electrode 34 illustrated in FIG. 1 bymeans of a conductor 36. Pace/sense circuitry 78 is also coupled toventricular electrode 28, illustrated in FIG. 1, by means of a conductor82, allowing for bipolar sensing of R-waves between electrodes 34 and 28and for delivery of bipolar pacing pulses between electrodes 34 and 28,as discussed above.

FIGS. 3(a) through 3(g) show perspective views of various components ofICD IPG 10, including one embodiment of the capacitor of the presentinvention, as those components are placed successively within thehousing of ICD IPG 10 comprising right and left hand shields 240 and350.

In FIG. 3(a), electronics module 360 is placed in right-hand shield 340of ICD IPG 10. FIG. 3(b) shows ICD IPG 10 once electronics module 360has been seated in right-hand shield 340.

FIG. 3(c) shows a pair of capacitors 265 fabricated as described hereinprior to being placed within right-hand shield 340, the capacitors 265being connected electrically in series by interconnections inelectronics module 340. FIG. 3(d) shows ICD IPG 10 once the pair ofcapacitors 265 has been placed within right-hand shield 340. It will beunderstood that other shapes of capacitors 265 can be inserted into thehousing of ICD IPG 10 in the same or similar manner as described here.

FIG. 3(e) shows insulator cup 370 prior to its placing atop capacitors265 in right-hand shield 340. FIG. 3(f) shows electrochemical cell orbattery 380 having insulator 382 disposed around battery 380 prior toplacing it in shield 340. Battery 380 provides the electrical energyrequired to charge and re-charge capacitors 265, and also powerselectronics module 360. Battery 380 may take any of the forms employedin the prior art to provide cardioversion/defibrillation energy, some ofwhich are identified in above referenced, commonly assigned, '133patent.

FIG. 3(h) shows ICD IPG 10 having left-hand shield 350 connected toright-hand shield 340 and feedthrough 390 projecting upwardly from bothshield halves. Activity sensor 400 and patient alert apparatus 410 areshown disposed on the side lower portion of left-hand shield 350.Left-hand shield 350 and right-hand shield 340 are subsequently closedand hermetically sealed (not shown in the figures).

FIG. 4 shows an exploded view of one embodiment of an anode-cathodesub-assembly or capacitor layer 227 of capacitor 265 in which thepresent invention may be implemented. It will be understood that theteachings of the present invention can be employed in the fabrication ofand in the resulting capacitors employing a single cathode layer, asingle anode layer formed of a plurality of anode sheets assembledtogether and to an anode tab as described herein, and a separatorseparating the anode layer and cathode layer.

The exemplary capacitor layer 227 comprises alternating substantiallyrectangular-shaped anode layers 170 and cathode layers 175, with asubstantially rectangular-shaped separator layer 180 being interposedtherebetween. The shapes of anode layers 170, cathode layers 175 andseparator layers 180 are primarily a matter of design choice, and aredictated largely by the shape or configuration of case 90 within whichthose layers are ultimately disposed. Anode layers 170, cathode layers175 and separator layers 180 may assume any arbitrary shape to optimizepackaging efficiency.

Exemplary anode layer 170 d most preferably comprises a plurality ofnon-notched anode sheets 185 designated 185 a, 185 b, 185 c and notchedanode sheet 190, including anode tab notch 200, that are laser weldedtogether in accordance with the present invention and anode tab 195fitted into tab notch 200 and laser welded to most or all of the anodesheets 185 a, 18 b, 185 c in accordance with another aspect of thepresent invention. It will be understood that anode layer 170 d shown inFIG. 4 is but one possible embodiment of an anode layer 170. Exemplarycathode layer 175 d most preferably is a single sheet of aluminum foilhaving a cathode tab 176 projecting from the periphery or edge thereof.

Individual anode sheets 185 a, 185 b, 190 and 185 c (alternativelyreferred to as anode sheets 185/190 herein) are cut from high-purityaluminum “formed” as described above to achieve high capacitance perunit area. Thin anode sheets 185/190 are preferred, especially if theysubstantially maintain or increase specific capacitance while reducingthe thickness of the electrode stack assembly 225 or maintain thethickness of electrode stack assembly 225 while increasing overallcapacitance. For example, it is contemplated that individual anodesheets 185/190 have a thickness of between about 10 micrometers andabout 500 micrometers.

Cathode layer 175 is preferably a single sheet cut from high purity,flexible, aluminum foil. Cathode layer 175 is most preferably cut fromaluminum foil having high surface area (i.e., highly etched cathodefoil), high specific capacitance (preferably at least 200microfarads/cm², and at least 250 microfarads/cm² when fresh), athickness of about 30 micrometers, a cleanliness of about 1.0 mg/m²respecting projected area maximum chloride contamination, and a puritywhich may be less than corresponding to the starting foil material fromwhich anode foil is made. The cathode foil preferably has an initialpurity of at least 99% aluminum, and more preferably yet of about 99.4%aluminum, a final thickness of about 30 micrometers, and an initialspecific capacitance of about 250 microfarads per square centimeter. Inother embodiments, the cathode foil has a specific capacitance rangingbetween about 100 and about 500 microfarads/cm², and a thickness rangingbetween about 10 and about 150 micrometers.

It is generally preferred that the specific capacitance of the cathodefoil be as high as possible, and that cathode layer 175 be as thin aspossible. For example, it is contemplated that individual cathode layers175 have a specific capacitance of about 100-1,000 microfarads/cm².Suitable cathode foils are commercially available on a widespread basis.In still other embodiments, the cathode foil comprises materials ormetals in addition to aluminum, aluminum alloys and “pure” aluminum.

Separator layer sheets 180 a and 180 b and outer separator layers of theelectrode stack assembly 225 (FIG. 9) assembled from a plurality ofstacked capacitor layers 227 are most preferably made from a roll orsheet of separator material. Separator layers 180 are preferably cutslightly larger than anode layers 170 and cathode layers 175 toaccommodate misalignment during the stacking of layers, to preventsubsequent shorting between anode and cathode layers, and to otherwiseensure that a physical barrier is disposed between the anodes and thecathodes of the finished capacitor.

In one preferred embodiment of the capacitor layer 227 as depicted inFIG. 4, two individual separator layer sheets 180 a and 180 b form theseparator layer 180 that is disposed between each anode layer 170 andcathode layer 175. Further single separator layer sheets 180 a and 180 bare disposed against the outer surfaces of the anode sheet 185 c and thecathode layer 175 d. When the sub-assemblies are stacked, the outermostsingle separator layer sheets 180 a and 180 b bear against adjacentoutermost single separator layer sheets 180 b and 180 a, respectively,of adjacent capacitor layers so that two sheet separator layers 180separate all adjacent cathode and anode layers of an electrode stackassembly 225.

It is preferred that separator layer sheets 180 a and 180 b and exteriorseparator layers between the electrode stack assembly and the case andcover be fabricated of a material that: (a) is chemically inert; (b) ischemically compatible with the selected electrolyte; (c) may beimpregnated with the electrolyte to produce a low resistance pathbetween adjoining anode and cathode layers, and (d) physically separatesadjoining anode and cathode layers. In one preferred embodiment,separator material is a pure cellulose, very low halide or chloridecontent Kraft paper having a thickness of about 0.0005 inches, a densityof about 1.06 grams/cm³, a dielectric strength of 1,400 Volts AC per0.001 inches thickness, and a low number of conducting paths (about0.4/ft² or less). Separator layer sheets 180 a and 180 b and outerseparator layers 165 a and 165 b may also be cut from materials otherthan Kraft paper, such as Manila paper, porous polymeric materials orfabric gauze materials. In such capacitor stacks assembled of aplurality of capacitor layers, a liquid electrolyte saturates or wetsseparator layers 180 and is disposed within the capacitor interior casechamber.

It will be understood by those skilled in the art that the precisenumber of capacitor layers 227 selected for use in a electrode stackassembly 225 will depend upon the energy density, volume, voltage,current, energy output and other requirements placed upon capacitor 265.Similarly, it will be understood by those skilled in the art that theprecise number of notched anode sheets 190 and un-notched anode sheets185, anode tabs 195, anode layers 170, cathode layers 175 and separatorlayers 180 selected for use in a given embodiment of capacitor layer 227will depend upon the energy density, volume, voltage, current, energyoutput and other requirements placed upon capacitor 265. It will nowbecome apparent that a virtually unlimited number of combinations andpermutations respecting the number of capacitor layers 227, and thenumber of notched anode sheets 190 and un-notched anode sheets 185forming anode layer 170, anode layers 170, anode tabs 195, cathodelayers 175 and separator layers 180 disposed within each capacitor layer227, may be selected according to the particular requirements ofcapacitor 265. In particular, while the described preferred embodimentof the invention relates to use of four anode sheets 185 a, 185 b, 185c, and 190, it will be appreciated that a larger or smaller number ofanode sheets can be joined together to form an anode layer employing theteachings of the present invention.

FIG. 5 depicts the method of forming anode sheets, attaching the anodesheets together to form an anode layer and then fabricating anelectrolytic capacitor using the anode layers. First, a thin aluminumfoil of the type described above is provided in step S100, etched instep S102, “formed” in step S104, and cut into anode sheets 185/190shown in FIG. 4 in step S106. The anodized, aluminum oxide, dielectriclayers are grown or “formed” in step S104 over the pores and the tunnelscreated in the etching step S102 in a manner known in the art.

The anode sheets 185/190 have opposed major anode sheet surfaces thatcan be highly etched in step S102 to form certain pores extending partway through the thickness of anode sheet to a sheet core layer andcertain through-etched tunnels extending all the way through the sheetcore layer to provide electrolyte wetting through the outer anode sheetsto inner anode sheets of an anode layer. The large pores, small pores,large cross-section tunnels, and small cross-section tunnels provideenhanced surface area in comparison to the planar sheet surfaces priorto etching. However, some surface area potential is lost by virtue ofoverly large pores and tunnels. Conversely, ESR is increased by smalltunnels that impede electrolyte and ion passage therethrough.Preferably, the etched anode foil has a high specific capacitance (atleast about 0.3, at least about 0.5 or most preferably at least about0.8 microfarads/cm²), has a dielectric withstand parameter of at least425 Volts DC, a thickness ranging between about 50 and about 200micrometers, and a cleanliness of about 1.0 mg/m² respecting projectedarea maximum chloride contamination. The anode foil preferably has arated surge voltage of 390 Volts, an initial purity of about 99.99%aluminum, a final thickness of about 104 micrometers, plus or minusabout five micrometers, and a specific capacitance of about 0.8microfarads per square centimeter. Suitable anode foils etched tospecification are commercially available on a widespread basis.

The anode and cathode sheets are most preferably cut to shape in stepS106 using dies having low wall-to-wall clearance, where inter-wallspacing between the substantially vertically-oriented correspondingwalls of the punch and die is most preferably on the order of about 6millionths of an inch per side. Larger or smaller inter-wall spacingsbetween the substantially vertically oriented corresponding walls of thepunch and cavity, such as about 2-12 millionths of an inch may also beemployed but are less preferred. The anode tab 195 d is preferably cutfrom aluminum foil, and separator layers 180 a, 180 b are preferably cutfrom Kraft paper, respectively, in the same manner.

Such low clearance results in smooth, burr free edges along theperipheries of anode sheets 185 and 190 and anode tabs 195 as well ascathode layers 175, cathode tabs 176 and the separator layers 180 a, 180b of each capacitor layer 170. Smooth, burr free edges on the walls ofthe dies have been discovered to be critical respecting reliableperformance of a capacitor. The presence of burrs along the peripheriesof anode sheets 185 and 190, anode and cathode tabs 195, 176, cathodelayers 175 and separator layers 180 may result in short circuit andfailure of the capacitor. The means by which anode foil, cathode foil,and separator materials are cut may have a significant impact on thelack or presence of burrs and other cutting debris disposed about theperipheries of the cut members. The use of low clearance dies producesan edge superior to the edge produced by other cutting methods, such assteel rule dies. The shape, flexibility and speed of a low clearance diehave been discovered to be superior to those achieved by laser or bladecutting. Other methods of cutting or forming anode sheets 185 and 190,anode tabs 195, cathode layers 175 and separator layers 180 include, butare not limited to, steel rule die cutting, laser cutting, water jetcutting and blade cutting. Further details relating to preferred methodsof cutting the anode foil to form anode sheets and sandwiching anodesheets together to form an anode layer 170 are set forth in theabove-referenced, commonly assigned, '133 patent.

In one embodiment of the invention, the anode tab 195 is attached instep S108 by cold welding the portion of the anode tab 195 fitted intothe notch 200 to the anode sheets 185 am 185 b, 185 c. The tab notch 200can be at in the edge of the notched anode sheet 190 such that an outerside edge of the anode tab 195 is aligned with the edges of the anodesheets 185 a, 185 b, 185 c or can be a slot extending into the notchedanode sheet 190.

But in the preferred practice of the invention, the tab notch 200 is atin the edge of the notched anode sheet 190, and the anode tab 195 issimply positioned in the notch 200 in step S108 such that an outer sideedge of the anode tab 195 is aligned with the edges of the anode sheets185 a, 185 b, 185 c. The anode sheets 185/190 and anode tab 195 arestacked in a laser weld fixture or bed S110 so that the sheet edges arein alignment and slight pressure is applied to the stacked anode sheets185/190 to maintain the etched and oxidized layers in close contactwithin prescribed stack thickness tolerances.

Then, laser welding beams are applied to the sheet edges of the anodesheets in all embodiments, and optionally across the exposed edge of theanode tab and the other anode sheets in step S114 to melt the etched andanodized and valve metal core layers, e.g., aluminum, together. In thisway, several laser weld beads are made across the aligned sheets (andtab) that mechanically and electrically form the anode layer 170 d orthe alternative anode layer 270 d shown in FIGS. 7 and 8 as describedfurther below.

Thus, in reference to FIG. 6, the anode layer 170 d is fitted into thefixture (not shown) in relation to a plurality of stationary laser lightsources 312, 322, 332, 342 that apply the laser beams 314, 324, 334,344, respectively to the stacked anode sheet edges forming the anodelayer edge 172 between the major anode layer surfaces 174 and 178. Thelaser beams 314, 324, 334, 344 melt edge bands or lines of the valvemetal to form weld beads 316, 326, 336, 346 across the attached anodesheet edges to form an anode layer edge. The weld beads 316, 326, 336,346 can have any suitable width and depth that is effective to make theelectrical and mechanical attachment without unduly reducing thecapacitance by reducing the etched and anodized volume of the valvemetal.

It will be understood that a greater or lesser number of laser lightsources can be employed to form the weld beads. Furthermore, it will beunderstood that a single laser light source can be substituted for theseparate laser light sources 312, 322, 332, 342 with a carriage forrotating the fixture and the aligned anode sheet edges into positions tomake the specified number of weld beads at specified locations.

A larger number of anode sheets than the four anode sheets 185/190 canbe stacked and welded together in this manner of steps S100-S112 asshown in FIGS. 7 and 8 as well as FIG. 13 described below. Thus, inthese exemplary embodiments depicted in FIGS. 7 and 8, seven anodesheets 285 a-285 g and the notched anode sheet 290 (collectivelyreferred to as anode sheets 285/290) are laser welded by weld beadsextending across the anode layer edge 272. Weld beads 356 and 358 causedby the laser beam energy are depicted extending across all of the anodesheet edges forming anode layer edge 272 extending between the anodelayer major surfaces 274 and 276.

The weld beads 352 and 354 also extend across the anode tab 295 d fittedinto the tab notch 300 of the notched anode sheet 290. In theseembodiments, the weld beads 352 and 354 extend across the aligned edgesof the tab 295 d and the anode sheets 285 a-285 g in step S112. The weldbeads 352, 354 could extend all the way across the anode edge 272 to theanode layer sides 274 and 276.

The weld beads extending across the aligned edges of the anode layers170 d and 270 d can be reinforced by cutting the edges of the anodesheets 185/190 and 285/290 in step S104 to have edge weld notches forreceiving one or more valve metal wire or strip and then laser weldingthe laser weld beads over the received valve metal wires or strips. Forexample, the anode layer 270 d of FIG. 7 is modified as the anode layer270 d′ of FIG. 8(a) by cutting anode edge weld notches 283 and 287 ineach of the anode sheets 285/290 that, when aligned, extend across theanode layer edge 272 between the anode layer sides 274 and 276 atpredetermined places along the anode layer edge 272. In this example,flat weld wires 293 and 297 are fitted into the anode edge weld notches283 and 287 in step S110, and the laser beams are applied along the flatweld wires 293 and 297 in the edge weld notches 283 and 287 to melt theadjacent exposed anode sheet edges of node sheets 285/290 against thewires 293 and 297. The weld wires 293 and 297 can be strips of the samevalve metal foil as the valve metal foil anode sheets 285/290 and tab295 d, e.g., aluminum foil. The laser energy can melt the flat weldwires 293 and 297 and the adjacent valve metal of the core layers of theanode sheets 285/290 to form the weld beads 356′ and 358′. This samereinforcement technique can be employed to reinforce the weld beads 352and 354. It will be understood that the reinforcing weld wire 293, 297in each weld notch can have other cross-sections, and the cross-sectionof the weld notches 283 and 287 can be selected to receive suchreinforcing weld wire or wires.

FIG. 8(b) is a partial end schematic illustration of a variation of FIG.8(a) wherein the weld beads each can comprise a pair of weld beadsformed of melt portions of the wire in the aligned weld notches and theadjoining anode sheet edges. For example, the edge weld notch 283 a issubstantially square and receives a round weld wire 293 a. The weld bead356 comprises a pair of weld beads 356 a and 356 b that shownschematically as melted valve metal, e.g., aluminum, from corners of theanode sheets at the weld notch 283 a and from the weld wire 293 a.

FIGS. 9 and 10 illustrate the formation of the electrode stack assembly225 in accordance with step S112 of FIG. 5 in relation to the capacitorcase cover 110, the case housing 90 and other components of thecapacitor 265.

The electrode stack assembly 225 comprises a plurality of capacitorlayers 227 a-227 h assembled as described above with reference to FIG. 4and having anode tabs 195 a-195 h and cathode tabs 176 a-176 h. Thevoltage developed across each capacitor layer disposed within electrodestack assembly 225 most preferably ranges between about 360 and about390 Volts DC. As described below, the various anode sub-assemblies ofelectrode stack assembly 225 are typically connected in parallelelectrically, as are the various cathode layers of electrode stackassembly 225. The electrode stack assembly 225 is merely illustrative,and does not limit the scope of the present invention in any wayrespecting the number or combination of anode layers 170, cathode layers175, separator layers 180, anode tabs 195, cathode tabs 176, and so on.The number of electrode components is instead determined according tothe total capacitance required, the total area of each layer, thespecific capacitance of the foil employed and other factors.

The capacitor layers 227 a 227 h are stacked together between outerpaper layers 165 a and 165 b, and outer wrap 115 is folded over the topof electrode stack assembly 225 in step S112. Wrapping tape 245 is thenholds outer wrap 115 in place and secures the various components ofelectrode stack assembly 225 together. Outer wrap 115 is most preferablydie cut from separator material described above or other suitablematerials such as polymeric materials, suitable heat shrink materials,suitable rubberized materials and synthetic equivalents or derivativesthereof, and the like. Wrapping tape 245 is most preferably cut from apolypropylene-backed acrylic adhesive tape, but may also be replaced bya staple, an ultrasonic paper joint or weld, suitable adhesives otherthan acrylic adhesive, suitable tape other than polypropylene-backedtape, a hook and corresponding clasp and so on. Usable alternatives toouter wrap 115 and wrapping tape 245 and various stacking andregistration processes by which electrode stack assembly 225 is mostpreferably made are not material to the present invention and aredisclosed in the above-referenced, commonly assigned, '133 patent.

FIG. 10 shows an exploded top perspective view of one embodiment of anexemplary, case neutral, electrolytic capacitor 265 employing theelectrode stack assembly 225 therein and the electrical connections madeto the gathered anode and cathode tabs 232 and 233. This embodimentincludes anode feedthrough 120 and cathode feedthrough 125 mostpreferably having coiled basal portions 121 and 126, respectively.Feedthroughs 120 and 125 provide electrical feedthrough terminals forcapacitor 265 and gather gathered anode tabs 232 and gathered cathodetabs 233 within basal portions 121 and 126 for electrical and mechanicalinterconnection.

Feedthrough wire is first provided and trimmed to length forconstruction of feedthroughs 120 and 125. One end of the trimmed wire iscoiled such that its inside diameter or dimension is slightly largerthan the diameter or dimension required to encircle gathered anode tabs232 or gathered cathode tabs 233. Gathered anode tabs 232 are nextgathered, or brought together in a bundle by crimping, and insidediameter 131 of anode feedthrough coil assembly 120 is placed overgathered anode tabs 232 such that anode feedthrough pin 130 extendsoutwardly away from the base of gathered anode tabs 232. Similarly,gathered cathode tabs 233 are gathered and inside diameter 136 ofcathode feedthrough coil assembly 125 is placed over gathered cathodetabs 233 such that cathode feedthrough pin 135 extends outwardly awayfrom the base of cathode tab 233. Coiled basal portions 121 and 126 ofanode and cathode feedthroughs 120 and 125 are then most preferablycrimped onto anode and cathode tabs 232 and 233, followed by trimmingthe distal ends thereof, most preferably such that the crimps areoriented substantially perpendicular to imaginary axes 234 and 235 ofgathered anode and cathode tabs 232 and 233. Trimming the distal endsmay also, but less preferably, be accomplished at othernon-perpendicular angles respecting imaginary axes 234 and 235.

In some preferred methods, a crimping force is applied to feedthroughcoils 121 and 126 and tabs 232 and 233 throughout a subsequent preferredwelding step. In one method, it is preferred that the crimped anode andcathode feedthroughs be laser or ultrasonically welded along the topportion of the trimmed edge of the distal ends to anode and cathode tabs232 and 233. Following welding of feedthroughs 120 and 125 to gatheredanode tabs 232 and gathered cathode tabs 233, respectively, pins 130 and135 are bent for insertion through feedthrough holes 142 and 143 of case90.

Many different embodiments of the feedthroughs and means for connectingthe feedthrough pins to anode and cathode tabs exist other than thoseshown explicitly in the figures and are described in theabove-referenced, commonly assigned, '133 patent.

A case sub-assembly is also created from case 90, anode ferrule 95,cathode ferrule 100, and fill port ferrule 105 are first provided. In apreferred embodiment of capacitor 265, the case 90 and cover 110 arefabricated of aluminum. In other embodiments, case 90 or cover 110 maybe fabricated of any other suitable corrosion-resistant metal such astitanium or stainless steel, or may alternatively be fabricated of asuitable plastic, polymeric material or ceramic. The anode ferrule 95and cathode ferrule 100 are welded to the aluminum case side wall to fitaround anode and cathode feedthrough ferrule holes 142 and 143, and afill port ferrule is welded to the case side wall around a fill porthole 106. The welding steps form no part of the present invention andvarious ways of doing so are disclosed in detail in theabove-referenced, commonly assigned, '133 patent.

Wire guides 140 and 141 fit within center holes of ferrules 95 and 100respectively and receive, center, and electrically insulate anode andcathode pins 130 and 135 from the case 90, anode ferrule 95, and cathodeferrule 100. The formation and assembly of the wire guides 140, 141 withthe ferrules 95, 100 and cathode pins 130, 135 form no part of thepresent invention and examples thereof are disclosed in detail in theabove-referenced, commonly assigned, '133 patent. Similarly, theinsertion of the cathode pins 130, 135 through the wire guides 140, 141and the seating of the electrode stack assembly 225 coupled thereto intothe interior case chamber of case 90 form no part of the presentinvention and examples thereof are disclosed in detail in theabove-referenced, commonly assigned, '133 patent.

A connector assembly is also coupled with the exposed, outwardlyextending pins 130 and 135. In one preferred embodiment, connector block145 is disposed atop or otherwise connected to case 90 and/or cover 110,and has wire harness 155 attached thereto and potting adhesive disposedtherein. However, the particular configuration of connector block 145and its method of fabrication do not play a role in the practice of thepresent invention. Examples thereof are disclosed in detail in theabove-referenced, commonly assigned, '133 patent.

In the illustrated embodiment, pre-formed plastic connector block 145 isplaced on anode ferrule 95 and cathode ferrule 100 by guiding anodefeedthrough pin 130 through connector block anode feedthrough hole 300,and then guiding cathode feedthrough pin 135 through connector blockcathode feedthrough hole 305. Connector block 145 is next seated flushagainst the exterior surface of case 90. Anode feedthrough pin 130 isthen inserted into anode crimp tube 150 b of wire harness 155. Cathodefeedthrough pin 135 is then inserted into cathode crimp tube 150 a ofwire harness 155. Crimp tubes 150 a and 150 b are then crimped tofeedthrough pins 130 and 135. The distal or basal portions of crimptubes 150 a and 150 b are crimped on insulated anode lead 151 andinsulated cathode lead 152, respectively. An epoxy adhesive is theninjected into voids in the connector block 145 to insulate the crimpedconnections, seal the wire guides 140 and 141, case 90 and ferrules 95and 100, and provide strain relief to feedthrough pins 130 and 135 andto the feedthrough wire crimp connections. Insulated leads 151 and 152are likewise connected to terminal connector 153 that forms the femaleend of a slide contact and is adapted to be connected to electronicsmodule 360 in FIG. 3(d). The completed assembly is depicted in FIG. 11.

The life of capacitor 265 may be appreciably shortened if solvent vaporor electrolyte fluid escapes from the interior of capacitor 265.Moreover, if capacitor 265 leaks electrolyte, the electrolyte may attackthe circuits to which capacitor 265 is connected, or may even provide aconductive pathway between portions of that circuit. The cover 110 isplaced upon the upper edge 92 of the case side wall, the upper edge 92is crimped over the cover edge, and the joint therebetween is laserwelded all in a manner disclosed in the above-referenced '133 patent,for example, that forms no part of the present invention. The resultingcapacitor 265 depicted in FIG. 12 thus most preferably includes hermeticlaser welded seams between joint case 90 and cover 110, and betweenferrules 95, 100, and 105 and case 90. Additionally, anode feedthroughportion 236 and cathode feedthrough portion 240 most preferably have anadhesive seal disposed therein for sealing the ferrule walls and thefeedthrough wires.

The interior of capacitor 265 not occupied by the electrode stackassembly 225 is filled with electrolyte through the fill port 107 weldedat fill port ferrule 105 into hole 106, aging cycles are conducted, andthe fill port is then closed. The filling and aging are accomplished ina plurality of vacuum impregnation cycles and aging cycles form no partof the present invention and examples thereof are disclosed in detail inthe above-referenced, commonly assigned, '133 patent. The electrolytemay be any suitable liquid electrolyte for high voltage electrolyticcapacitors. In a preferred embodiment of the present invention, theelectrolyte is an ethylene glycol based electrolyte having an adipicacid solute. It is contemplated that other liquid electrolytes suitablefor use in high voltage capacitors may also be employed.

During capacitor charging, the ethylene glycol based electrolytereleases hydrogen gas that accumulates within the interior capacitorchamber and eventually can cause the base and cover to bulge outward. Inaccordance with a preferred embodiment of the present invention,hydrogen gas is released through the lumen of fill port 107 while lossof liquid or vaporized electrolyte is prevented.

It will be understood that the capacitor 265 may alternatively befabricated as a case negative capacitor where case 90 and cover 110 areelectrically connected to the cathode layers and are therefore at thesame electrical potential as the cathode layers, i.e., at negativepotential.

The particular shape, number and manner of fabrication and formation ofthe anode sheets of the anode layers described herein is merelyillustrative, and does not limit the scope of the present invention inany way. Among other things, the present invention can be employed toelectrically and mechanically connect the valve metal cores of anynumber of stacked, etched and anodised, anode sheets and anyconfigurations of the anode sheets.

FIG. 13 depicts such a design of an alternative electrode stack assembly425 of an electrolytic capacitor in which the present invention can bepracticed. In this embodiment, a single anode layer 470 is fabricated ofa large number of formed anode sheets 485 stacked together into theshape of a block having an anode layer edge 472 extending all the wayaround the block and laser welded together along plural weld beads 416,426, 436, 446 across the anode layer edge 472. The laser welded anodelayer 470 is covered by a separator 480 that is in turn covered by acathode sheet 475. In this case, the anode sheets 485 are stacked onedge and laser welded so that the major surfaces are the exposed edgesof the anode sheets, and electrolyte permeates the pores and tunnels viathe exposed edges. Steps S100-S112 are followed as described above tolaser weld the anode sheets 485 along the weld beads 416, 426, 436, 446and along other weld beads concealed by the separator 480 and cathodesheet 475. The anode tab 495 can be laser welded coupled to the anodelayer 470 in the manner described above, and cathode tab 476 is formedintegrally with the cathode sheet 475. The electrode stack assembly 425can then be wrapped into a electrically insulating packaging and fittedinto and hermetically sealed within a suitably shaped and sizedcapacitor case in a manner similar to that described above or in any ofthe ways known in the art.

The preceding specific embodiments are illustrative of a capacitorstructure and method of fabrication thereof and its incorporation intoan IMD in accordance with the present invention. It is to be understood,therefore, that other expedients known to those skilled in the art ordisclosed herein, and existing prior to the filing date of thisapplication or coming into existence at a later time may be employedwithout departing from the invention or the scope of the appendedclaims.

All patents and printed publications disclosed herein are herebyincorporated by reference herein into the specification hereof, each inits respective entirety.

1. An electrode stack assembly of an electrolytic capacitor comprising:an anode layer comprising: a first anode sheet fabricated of a valvemetal having first and second sheet sides bounded by a sheet edge; atleast one second anode sheet fabricated of a valve metal having firstand second sheet sides bounded by a sheet edge, the second anode sheetand first anode sheet fitted side-by-side whereby at least a portion ofthe first and second anode sheet edges are substantially aligned tocomprise an anode layer edge; and a laser weld bead extending across theanode layer edge that electrically and mechanically couples the firstand second anode sheets together; a cathode layer; and a separatorinterposed between the anode layer and the cathode layer.
 2. Theelectrode stack assembly of claim 1, wherein the first anode sheetfurther comprises a tab notch extending into the first anode sheet edge,and further comprising: an anode tab comprising a first tab portionshaped to fit into the tab notch such that a second tab portion extendsoutwardly from the anode stack edge and a portion of an anode tab edgeis substantially aligned with a portion of the second anode sheet edge;and at least one laser bead extending across the substantially alignedanode tab edge and second anode sheet edge.
 3. The electrode stackassembly of claim 1, wherein the first anode sheet further comprises atab notch extending into the first anode sheet edge, and furthercomprising: a further second anode sheet, one second anode sheet locatedagainst the first sheet side of the first anode sheet and the othersecond anode sheet located against the second sheet side of the firstanode sheet; an anode tab comprising a first tab portion shaped to fitinto the tab notch such that a second tab portion extends outwardly fromthe anode stack edge and a portion of an anode tab edge is substantiallyaligned with a portion of the second anode sheet edge; and at least onelaser bead extending across the substantially aligned anode tab edge andsecond anode sheet edge.
 4. The electrode stack assembly of claim 1,wherein the first and second anode sheets are fabricated with weldnotches that are substantially aligned in an anode layer weld notch whenthe first and second anode sheets are fitted side-by-side, and the laserweld bead extends along the anode layer weld notch.
 5. The electrodestack assembly of claim 1, wherein the first and second anode sheets arefabricated with weld notches that are substantially aligned in an anodelayer weld notch when the first and second anode sheets are fittedside-by-side, weld wires are fitted into the weld notches, and the laserweld bead extends along the weld notch and the weld wire in the anodelayer weld notch joining the anode sheets along the anode layer weldnotch with the weld wire.
 6. The electrode stack assembly of claim 5,wherein the laser weld bead comprises a pair of laser weld beads joiningthe anode sheets at the anode layer weld notch with the weld wire.
 7. Anelectrode stack assembly of an electrolytic capacitor comprising: ananode layer comprising: a plurality of N anode sheets fabricated of avalve metal having first and second sheet sides that bounded by a sheetedge, the N anode sheets sheet fitted side-by-side whereby N−2 first andsecond sheet sides of the plurality of anode sheets are in mutualcontact and at least a portion of the first and second anode sheet edgesare substantially aligned to comprise an anode layer edge; and aplurality of laser weld beads extend across the anode layer edge at aplurality of locations along the anode layer edge that electrically andmechanically couples the N anode sheets together; a cathode layer; and aseparator between the anode layer and the cathode layer.
 8. Theelectrode stack assembly of claim 7, wherein at least one of the anodesheets further comprises a tab notch extending into the first anodesheet edge, and further comprising: an anode tab comprising a first tabportion shaped to fit into the tab notch such that a second tab portionextends outwardly from the anode stack edge and a portion of an anodetab edge is substantially aligned with a portion of the anode layeredge; and at least one laser bead extending across the substantiallyaligned anode tab edge and at least one or more anode sheet edge of theanode layer edge.
 9. The electrode stack assembly of claim 8, whereinthe N anode sheets are fabricated with weld notches that aresubstantially aligned in an anode layer weld notch when the N anodesheets are fitted side-by-side, weld wires are fitted into the anodelayer weld notches, and the laser weld bead extends along the anodelayer weld notch and the weld wire in the anode layer weld notch joiningthe anode sheets along the anode layer weld notch with the weld wire.10. The electrode stack assembly of claim 7, wherein the N anode sheetsare fabricated with weld notches that are substantially aligned in ananode layer weld notch when the N anode sheets are fitted side-by-side,weld wires are fitted into the anode layer weld notches, and the laserweld bead extends along the anode layer weld notch and the weld wire inthe anode layer weld notch joining the anode sheets along the anodelayer weld notch with the weld wire.
 11. The electrode stack assembly ofclaim 10, wherein the laser weld bead comprises a pair of laser weldbeads joining the anode sheets at the anode layer weld notch with theweld wire.
 12. The electrode stack assembly of claim 7, wherein the Nanode sheets are fabricated with weld notches that are substantiallyaligned in an anode layer weld notch when the N anode sheets are fittedside-by-side, and the laser weld bead extends along the anode layer weldnotch.
 13. A method of fabricating an electrode stack assembly of anelectrolytic capacitor comprising: fabricating an anode layer by:fabricating a first anode sheet of a valve metal having first and secondsheet sides that bounded by a sheet edge; fabricating at least onesecond anode sheet of a valve metal having first and second sheet sidesthat bounded by a sheet edge, fitting the second anode sheet and firstanode sheet side-by-side whereby at least a portion of the first andsecond anode sheet edges are substantially aligned to comprise an anodelayer edge; and laser welding a laser weld bead extending across theanode layer edge that electrically and mechanically couples the firstand second anode sheets together; fabricating a cathode layer; andinterposing a separator between the anode layer and the cathode layer.14. The method of claim 13, wherein the step of fabricating a firstanode sheet further comprises cutting a tab notch extending into thefirst anode sheet edge, and further comprising: in the fabricating step,fabricating a further second anode sheet of a valve metal having firstand second sheet sides that bounded by a sheet edge, in the fittingstep, fitting the further second anode sheet and first anode sheetside-by-side whereby at least a portion of the first and second anodesheet edges are substantially aligned to comprise the anode layer edge;and laser welding at least one laser bead extending across thesubstantially aligned anode tab edge and second anode sheet edge. 15.The method of claim 13, wherein the step of fabricating a first anodesheet further comprises cutting a tab notch extending into the firstanode sheet edge, and further comprising: in the fabricating step,fabricating a further second anode sheet of a valve metal having firstand second sheet sides that bounded by a sheet edge, in the fittingstep, fitting the further second anode sheet and first anode sheetside-by-side whereby at least a portion of the first and second anodesheet edges are substantially aligned to comprise the anode layer edge;fabricating an anode tab having a first tab portion shaped to fit intothe tab notch, a second tab portion shaped to extend outwardly from theanode stack edge and an anode tab edge; fitting the first tab portioninto the tab notch such that the second tab portion extends outwardlyfrom the anode stack edge and a portion of the anode tab edge issubstantially aligned with portions of the second anode sheet edges; andlaser welding at least one laser bead extending across the substantiallyaligned anode tab edge and second anode sheet edges.
 16. The method ofclaim 13, wherein: the steps of fabricating the first and second anodesheets further comprises fabricating the first and second anode sheetswith weld notches that are substantially aligned in an anode layer weldnotch when the first and second anode sheets are fitted side-by-side toform an anode layer weld notch; and the laser-welding step furthercomprises laser welding the weld bead extending along the anode layerweld notch.
 17. The method of claim 13, wherein: the steps offabricating the first and second anode sheets further comprisesfabricating the first and second anode sheets with weld notches that aresubstantially aligned in an anode layer weld notch when the first andsecond anode sheets are fitted side-by-side to form an anode layer weldnotch; and the laser welding step further comprises fitting a weld wireinto the anode layer weld notch, and laser welding the weld bead alongthe anode layer weld notch joining the anode sheets along the anodelayer weld notch with the weld wire.
 18. The method of claim 17, whereinthe laser welding step further comprises welding a pair of laser weldbeads joining the anode sheets along the anode layer weld notch with theweld wire.
 19. A method of fabricating an electrode stack assembly of anelectrolytic capacitor comprising: fabricating an anode layer by:fabricating a plurality of N anode sheets of a valve metal having firstand second sheet sides that bounded by a sheet edge; fitting the N anodesheets sheet side-by-side whereby N−2 first and second sheet sides ofthe plurality of anode sheets are in mutual contact and at least aportion of the first and second anode sheet edges are substantiallyaligned to comprise an anode layer edge; and laser welding at least onelaser weld bead across the anode layer edge at a location along theanode layer edge that electrically and mechanically couples the N anodesheets together; fabricating a cathode layer; and interposing aseparator between the anode layer and the cathode layer.
 20. The methodof claim 19, wherein the anode layer fabricating step further comprises:in the anode sheet fabricating step, fabricating at least one of theanode sheets with a tab notch extending into the first anode sheet edge,and further comprising: fabricating an anode tab comprising a first tabportion shaped to fit into the tab notch, a second tab portion shapedextends outwardly from the anode stack edge, and an anode tab edge; inthe fitting step, fitting the first tab portion into the tab notch suchthat the second tab portion extends outwardly from the anode stack edgeand a portion of an anode tab edge is substantially aligned with theportion of the anode layer edge; and laser welding at least one laserbead extending across the substantially aligned anode tab edge and atleast one or more anode sheet edge of the anode layer edge.
 21. Themethod of claim 20, wherein the anode layer fabricating step furthercomprises: in the anode sheet fabricating step, fabricating the N anodesheets with weld notches that are substantially aligned in an anodelayer weld notch when the N anode sheets are fitted side-by-side in thefitting step; and the laser-welding step comprises laser welding thelaser weld bead along the anode layer weld notch.
 22. The method ofclaim 19, wherein the anode layer fabricating step further comprises: inthe anode sheet fabricating step, fabricating the N anode sheets withweld notches that are substantially aligned in an anode layer weld notchwhen the N anode sheets are fitted side-by-side in the fitting step; andthe laser-welding step comprises laser welding the laser weld bead alongthe anode layer weld notch.
 23. The method of claim 19, wherein theanode layer fabricating step further comprises: in the anode sheetfabricating step, fabricating the N anode sheets with weld notches thatare substantially aligned in an anode layer weld notch when the N anodesheets are fitted side-by-side in the fitting step; and in the laserwelding step, fitting a weld wire into the anode layer weld notch, andlaser welding the laser weld bead along the anode layer weld notchjoining the anode sheets along the anode layer weld notch with the weldwire.
 24. The method of claim 19, wherein the anode layer fabricatingstep further comprises: in the anode sheet fabricating step, fabricatingthe N anode sheets with weld notches that are substantially aligned inan anode layer weld notch when the N anode sheets are fittedside-by-side in the fitting step; and in the laser welding step, fittinga weld wire into the anode layer weld notch, and laser welding the laserweld bead as a pair of laser weld beads joining the anode sheets alongthe anode weld notch with the weld wire.